Conventionally, gasification and ash melting systems are known as technologies which can be widely used for treating wastes such as not only municipal wastes, but also noncombustible wastes, burned residues, sludge, buried wastes. Such a gasification and ash melting system includes a gasification furnace which pyrolyzes and gasifies the wastes, a melting furnace that is provided at a downstream side of the gasification furnace, burns a pyrolysis gas generated in the gasification furnace at a high temperature, and converts ash in the gas into a molten slag, and a secondary combustion chamber in which an exhaust gas discharged from the melting furnace is burnt. To convert the wastes into a resource, to melt the wastes less, and to render the wastes harmless, the slag is extracted from the melting furnace and is recycled as construction materials such as a road bed material, or waste heat is recovered from the exhaust gas discharged from the secondary combustion chamber and produces electric power.
In the gasification furnace of this gasification and ash melting system, a fluidized bed gasification furnace is frequently used. The fluidized bed gasification furnace is a device in which a fluidized bed is formed by feeding combustion gas to a bottom of the furnace to fluidize a fluidization medium, which partially burns the wastes charged into the fluidized bed, and pyrolyzes the wastes in the fluidized bed which is maintained at a high temperature by the heat of combustion.
In the fluidized bed gasification furnace, the stabilization of fluidization of the fluidization medium is required. The fluidized bed gasification furnace is disclosed in Patent Literature 1 in which, to stabilize the fluidization of the fluidization medium, a defective fluidization spot is identified based on results detected by a plurality of temperature sensors installed in the furnace, and more combustion gas is fed to the defective fluidization spot.